The present invention relates to image reading apparatuses such as a scanner for optically reading a draft, and image forming apparatuses such as a digital copying machine for forming an image of the draft read by the image reading apparatus.
In a conventional image forming apparatus, a copied image of a draft with a plurality of types of images intermingled therein has been outputted by a plurality of scanning operations.
On the other hand, in Jpn. Pat. Appln. KOKAI Publication No. 8-88766, various types of information on an image type and image position information are acquired during a forward scanning operation, and an image processing suitable for each image type is performed based on the information during a return scanning operation.
Moreover, in Jpn. Pat. Appln. KOKAI Publication No. 2000-307821, a constitution is disclosed in which a three line colors CCD sensor is used, and which has a sheet through system for reading a draft being conveyed and a flat bed system for reading the draft laid on a draft bed. For a black-and-white image, image data (R signal, G signal, and B signal for three lines are synthesized) read by the sheet through system is outputted. For a color image, the same draft is subsequently laid on the draft bed and image data (R, G, B signals) read by the flat bed system is outputted.
The sheet through system is suitable for high-speed reading, because the draft can continuously be fed into a reading section at a high speed. However, the system is not suitable for reading of the color draft because it is difficult to control conveyance of the draft at a high precision.
Moreover, the flat bed system is not suitable for high-speed reading, because it is necessary to move the reading section having a considerable weight. However, the system is suitable for the reading of the color draft, because it is easy to control movement at a high precision.
However, when the black-and-white image is read by the sheet through system, the R, G, and B signals are synthesized. There is therefore a problem that a signal error is generated, an image quality is deteriorated, and high-precision and high-speed reading cannot be performed.
Furthermore, there is a demand for realization of the high-speed reading even with a draft in which a plurality of types of images are intermingled.